The present invention relates to processes for the production of high strength hollow rayon fibers or filaments which will recover their hollow condition after being immersed in water and in a preferable embodiment are substantially irreversible in that they remain hollow and do not collapse even after repeated drying and washing cycles. The invention relates also to the hollow rayon fibers produced.
Hollow rayon fibers are known to the prior art. They have a number of known uses in the production of paper and non-woven products. They have been produced by incorporating a blowing agent, such as sodium carbonate or sodium bicarbonate, into the viscose solution after the xanthation stage in the viscose rayon process. In the prior art processes, the viscose, containing the blowing agent, is spun into the conventional acidic spin bath whereby carbon dioxide gas is liberated from the blowing agent causing the fibers to blow or expand to several times their natural diameter. A number of patents disclose processes of this type and they have in common the shortcoming that when the fibers or filaments are dried, the fiber walls collapse and, in most instances, hydrogen bond together to form a flat, ribbon-like fiber. It has been the desire of the rayon industry for some time to provide hollow rayon fibers which would not collapse upon drying and which will retain their hollow configuration for a very substantial number of washing and drying cycles.
Woodings U.S. Pat. No. 3,626,045 is a patent disclosing a method of blowing rayon fibers. It seeks to overcome the problem of fiber wall collapse upon drying by adding to the viscose prior to spinning of from 0.75 to 2.0% by weight of polyethylene glycol based on the weight of the cellulose. The hollow rayon fibers which result can be dried after being formed without collapsing. However, the product of the patent has other shortcomings.
In accordance with the present invention, the disadvantages of conventional prior art blown hollow rayon fibers have been overcome by unique conditions of the processes of the present invention. These parameters are defined in the examples.
Patents disclose various methods for making hollow fibers, but none of which applicant is aware teaches or suggests a means which provides a high strength hollow rayon fiber which is substantially irreversible in the sense that it will not collapse upon being dried. These patents include: British Pat. No. 945,306; British Pat. No. 1,393,778; and Freund U.S. Pat. No. 2,013,491.
British Pat. No. 488,500 discloses a process for producing hollow cellulose acetate fibers by extruding a solution of the acetate downward into a volatile solvent medium and in a complicated manner produces a hollow fiber.
Kajitani U.S. Pat. No. 3,418,405 discloses a process for producing flat viscose fibers by extruding blown viscose into a medium containing a modifier, and such modifier is polyethylene glycol. The whole purpose is to produce a hollow fiber which will very readily collapse and form a flat fiber. This is just the opposite of the purpose of the present invention.
French Pat. No. 1,143,666 discloses the use of adducts of ethylene glycol and phenol, including the adduct of 15 units of ethylene oxide per molecule of phenol, as a viscose modifier. The purpose of this is strictly to produce a high strength solid rayon fiber suitable for a tire yarn end use. Howsman U.S. Pat. Nos. 2,890,130 and 2,890,132 disclose similar adducts of ethylene oxide with cresol and lactams, respectively, for the same purpose. None of these patents is concerned with the preparation of hollow rayon fibers.
British Pat. No. 1,393,778 discloses the preparation of multi-lobal collapsed fibers, which is not what the present invention is concerned with, by a process which is quite different from that of the present invention.
Patents disclose the treatment of cellulosic products in one form or another with aldehydes, but none of which applicant is aware teaches or suggests a means which provides a hollow rayon fiber which is substantially irreversible in the sense that it will not collapse upon being dried. These patents are: Alles U.S. Pat. No. 2,123,493; Drisch U.S. Pat. No. 2,597,624; Spining U.S. Pat. No. 2,935,373; Elssner U.S. Pat. No. 3,007,766; Reeves et al. U.S. Pat. No. 3,046,079; Drisch U.S. Pat. No. 3,351,696; and Canadian Pat. No. 898,461.
Cotton et al. U.S. Pat. No. 3,622,261 discloses a process for fixing formaldehyde on cellulose with the aid of a carbamate so that a fabric made of the cellulose will retain its wash and wear characteristics. But nothing in the patent relates to hollow rayon fibers and their production.
In a paper entitled "Never-Dried Cotton Fibers" by J. L. Williams et al., Textile Research Journal, Vol. 44, No. 5, pp. 370-377 (May 1974), and in the authors' corresponding U.S. Pat. No. 3,907,499, the authors describe a treatment of cotton, which has never been dried, with a dilute solution of formaldehyde. The authors state that this treatment prevents the cotton fiber walls from hydrogen bonding and that a cotton fiber is obtained, which when submerged in water, after having been dried, would to an extent reswell to an open configuration. The treatment of the process does not prevent collapse of the cotton fibers upon drying. It merely permits reswelling when the dried cotton fibers are again wetted with water. The authors are in no way concerned with hollow rayon fibers or methods for their production.
The hollow fibers of rayon produced by the processes of the invention do not collapse even when dried and in a preferred embodiment will not collapse even when subjected to a sequence of drying and washing treatments. The processes also produce a uniformly large number of blown fibers such as more than 90 or 95%.
The fibers produced from the preferred embodiment of the processes not only have permanent hollowness, but also exhibit high strength and sufficient crimp to permit ease in carding. The fibers produced by the processes of the present invention have properties similar to commercial high wet modulus rayon and are approaching that of cotton. Fabrics made from the hollow rayon fibers in the preferred embodiment produced by the present invention exhibit excellent bulk coverage, a dye absorption equivalent to that of cotton, and an opacity that is duller than either rayon or bleached cotton. Thus, this fiber would require less dulling agents during production than regular rayon.
It is, accordingly, an objective of the present invention to provide an in-line process for producing hollow rayon fibers of high strength that have the property of resisting collapse even after drying and washing treatments and which have large continuous lumens.
It is also an object of the present invention to provide hollow rayon fibers that have high bulk or covering power such as are useful in producing non-wovens or garments employed for outer wear or as dialysis tubes.
It is a further object of the present invention to provide hollow rayon fibers that have a soft, comfortable hand and which will retain their hollow condition after being immersed in water and then dried.
It is another object of the present invention to provide hollow rayon fibers which have high moisture absorption, thermal insulation and dielectric properties.
It is another object of this invention to produce fibers of high strength having greater than 3 g/d tenacity when tested in a conditioned atmosphere and greater than 1.8 g/d when tested in a wet state.
Other objects will be apparent to those skilled in the art from the present description.